There are many currently-known electrical products generally designed to detect or monitor a weak signal, whether the signal is visual or optical, magnetic, auditory, pressure-based or any other sensory measurement. These products include, for example, night vision binoculars, camera systems designed to detect images in sub-optimal conditions and listening devices designed to detect weak or distant sounds. In each of these products (along with similar-use products), the quality of the final or target image depends not only upon the strength and quality of the signal coming from the target or object being detected, but also the ability to minimize the random “noise” generated in the electronics of the monitoring device. In an optical system, for example, this noise may be “dark current noise,” which includes what is referred to as 1/f noise, thermal noise from the photodetector and the preamplifier (known as “Johnson noise”) and noise caused when voltage is applied to the photodetector (known as “shot noise”). The greater the random noise inside a product is compared to the strength of the target signal, the poorer the quality of the final target image. If the internal noise is significant compared to the target signal, whether it is because the magnitude of the noise is so great or the strength of the target signal is very weak, it will detract from or blur the image within the system. And if the signal is weak and there is a lot of noise in the system, the final image can be completely hidden or obliterated.
The ratio of signal strength to the strength of electronic noise is referred to as the “signal-to-noise” ratio: The stronger the signal, the lower the noise; or, the higher the signal-to-noise ratio, the better is the quality of the image being shown. Currently-known products require that an input signal (e.g., light, magnetic field, vibration, sound, heat, pressure, etc.) being sensed by an appropriate detector must have a signal strength greater than the electrical noise (primarily coming from the detector and preamplifier in the system) of the input stage before it can be reliably detected and viewed. This means that the signal-to-noise ratio must be greater than 1.0 before sensing is possible.
There exists several currently-known ways, or techniques, to improve the signal-to-noise ratio in an effort to keep it greater than 1.0. These techniques include: (1) amplifying the input signal and (2) filtering out the noise. Both of these techniques, however, require knowledge of the input signal in advance, or some way to identify the signal. That is, with regard to the former technique, the input signal must be known or identifiable in order to amplify it without amplifying the electronic noise that surrounds it, and with regard to the latter, the input signal must also be known in order to distinguish it from the noise that is being blocked by the filter.
Currently-known methods for identifying an input or target signal include: (a) knowing the type of signal in advance; (b) having control over the input signal and coding it when it is transmitted, such as with signal modulation schemes; or (c) time-averaging techniques to detect repeating signals and distinguish them from non-repeating random noise. Obviously, if the signal to be detected is not known or controlled in advance, none of the above techniques, other than time-averaging, can be used.
However, even if used, time-averaging techniques are limited and impractical because time-averaging, in general, is a relatively slow process requiring many samples to effectively reduce the noise that exists. Finally, none of the currently-known techniques, including time-averaging, are effective for detecting short duration or transient images where there is insufficient data to analyze the signal.
The Present Invention overcomes the aforementioned shortcomings of the currently-known techniques, and provides drastically improved signal-to-noise ratios even in those situations where creation of the input signal is not controlled, where the input signal is not known, and in situations where the target signal is very weak compared to a strong background signal. In particular, the Present Invention allows one to place “tags,” or codes, on the input signal, when the input or target signal is not known in advance and no control over transmission of the target signal is available, such that background signals and noise can be effectively attenuated and filtered, while maintaining the integrity of the target signal. This provides a high signal-to-noise ratio and the detection of signals in a manner and having a quality that has heretofore never been obtainable.